Telephone system



June 9,- 1931. G. E. scHoMAKER E1' AL 1,809,071

TELEPHONE SYSTEM Filed April 28, 192e. 5 sheets-sheet .1

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5 Sheets-Sheet 2 TELEPHONE SYSTEM June 9,- 1931. G. E. scHoMAKER ET ALFiled April 28, 192e m n wad? I O IILI June 9,- 1931. G. E. s'cHo'MAKERET AL 1,809,071

TELEPHONE SYSTEM Filed April 28, 1928 5 Sheets-Sheet 5 -LInLr E :Deurnel En Y June 9,- 1931. G. E. scHoMAKER ETAL *1,809,071

TELEPHONE SYSTEM Filed April 28, 192e` 5 sheets-sheet 4 was F.' En nld.

June 9,- 1.931.

G. E. .scHoMAKER ET'AI,

TELEPHONE SYSTEM Filed April 28, l192e;

5 sheets-'sheet 5 Imran nrs Eanr'ss E. E chamakar' C005 am: h No. .3o

'En 'E' .Bauli Patented June 9, 1931 UNEEB STATES PTEN'F GFFECE GEORGEE. SCEOMAKER, OF SYDNEY, NEW SQUTH WALES, l'U'STRALIA, ROY F. GOULD, OF'CHICAGO, LLITOS, ASSG-NOBS TO RESERVE HOLDING COMPANY, OF KANSAS GTY,MESSUB, [a CQEPOlD- ATON OF DELLWAEE.

TELEP-QONE SYSTEB Sera The present invention relates to telephonesystems in general, but is concerned more particularly with thebranch-exchange equipment in a telephone system employing both main andbranch exchanges, although several features of the invention are notspeciiically limited thereto.

The invention has been applied to an automatic telephone systemincluding an automatic main exchange and an automatic branch exchangehaving an attendants cabinet located therein to enable an attendant atthe branch exchange to complete incoming calls and to set up connectionsfrom a branchexchange subscriber to a. main-exchange subscriber whenrequested to do so.

One object of the invention is the application of the so-called by-passmethod of operation to the branch-exchange switching apparatus so that asingle connector will suftice, this connector being used merely tooperate the lineswitch on the called line to cause it to seize the sametrunk previously seized by the calling lineswitch.

A features of the invention lies in the arrangement whereby each of theten trunks presided over by a master switch is normally connected to thecommon connector switch, but is disconnected therefrom and connectedinstead to an individual battery feed and holding relay as soon as aconnection has been set up over the trunk.

According to a further feature of the invention, the master switch isarranged so that it does not operate to preselect a new trunk when acall is made, but waits until the common connector has been operatedover the seized trunl-z to signal the subscriber on the called line andto operate the lineswitch on the called line to make connection with thecalling line through the trunk in use, whereupon the master switchoperates in the usual manner to preselect another idle trunk.

Another obj ect of the invention is the provision of a timing deviceindividual to the connector for freeing the connector automatically incase the subscriber has not dialled the complete number and caused theconnector to be freed when disconnected from the trunk as abovementioned.

273,469, and in Great Britain August 26, 1927.

According to a further feature of the i11- vention, the above-mentionedtiming device is released and started over again after the completenumber has been dialled in order to control the application of ringingcurrent and the regular release of the connector.

A special feature of the arrangement is that ringing current is4transmitted as soon as the connection has been completed7 only a shortpreliminary ring being given at that time. A moment later, the timingdevice causes a long ring to be transmitted to the called line. Thislong ring is useful in a private automatic exchange in order to locatethe substation that is being signalled when several substations arelocated close together, such as, for example, at adjacent desks in anAnother object of the invention is the production of suitablearrangements in a system of the foregoing character whereby certainsubscribers are permitted to call through to the main exchange, whilecalls from other substations to the main exchange vare barred.

rnother object of the invention is the provision of arrangements in theconnector for preventing the connecting up of a battery supply to atrunk line when a. connection is being made thereover to the mainexchange or to a certain local equipment (a code call machine forexample) while permitting a battery supply connection to be made in casethe call is a regular local call. This permits branch-exchangesubscribers to dial mainexchange numbers and special local numbers.

Ano-ther object of the invention is the provision of suitablearrangements in the incoming trunk lines for controlling the operationof they connector so that it will fail to causeY the battery supply tobe connected to a local trunk line in case the call is incoming to thebranch exchange from the main exchange, the arrangement being preferredwherein the transmitter in the branch exchange is energized from currenttransmitted over the inter-exchange trunk line from the main exchange.

Another object of the invention is the provision of suitablearrangements for enabling an attendant at an attenda-nts cabinetassociated with the inter-exchange trunk lines to answer and extendcalls incoming from the main exchange, to answer the calls incoming toher cabinet from the branch exchange, and to set up tail-totailconnections betwcenmainexchange and branch-exchange subscribers.

vAnother object of the invention is the provision of a` novelarrangement whereby both busy-tone current and dial-tone current aretransmitted to the connector from the tone equipment over the sameconductor, arrangements being provided Jfor causing the flow ot tonecurrent to be distinctly different at one time from the iiow of tonecurrent at the other time so as to differentiate between the dial toneand the busy tone.

There are other objects and features of the invention having to do i'orthe most partwith the circuitdetails necessary to carry out the objectsand features above mentioned. The various objects and features of theinvention will be understood best from a further perusal oi' thedescripti n in connection with the accompanying drawings.

Referring now to the drawings comprising Figs. l to 5, they shew eymeans ot the usual circuit diagrams a suiiicient amount of equipment ina telephone system involvng the features of the invention to enable thesame to be understood. More in particular, these drawings show equipmentlocated in a main exchange, indicated at the left in Fig. l, and theessential equipment of a branch exchange interconnected with the mainexchange by means of the trunl line TL, Fig. 1, and oth-v ers. Thebranch exchange may be considered as belonging to the type ordinarilydesignated as a private branch exchange, an attendant being located atthe branch exchange to vcomplete incoming calls byV ascertaining thenumber desired and controlling the operation at the automatic switchingequipment, outgoing calls being completed responsive to the diallingoperation on the part of the calling subscriber without the aid of thebranchsexchange attendant.

rThe apparatus shown in Fig. 1 includes the portion of the main-exchangeequipment at the left, and the trunk circuit TC at the right of theinterconnecting trunk line TL. In the lower part of Fig. l there isindicated cert-ain lreys and lamps located at the switchboard of theattendant and individual to the trunk circuit TC.

The remaining portion of the attendants equipment is indicated in Fig.il, which should be placed under Fig. 1 with the interconnecting linesin alignment. The keys and other apparatus in Fig. e are common to theseveral trunk circuits such as the trunk circuit TC, Fig. 1. Fig. lshows two so-called information trunks extending to the attendantsswitchboard from the local switching LS2 is individual to the trunk lineTL with which it is associated through the medium ot' the trunk circuitTC, Fig. 1, being connected with such trunk circuit by way of conductors125-l29.

Fig. 3 shows the single connector of the branch exchange having wipersB22-325. This connector, through the common conductors 219*22l, isnormally connected to each of the trunk lines accessible to thelineswitches, one et them being the one comprising conductors 226-229,Fig. 2. This connector has access to each of the lines and line switcheset the branch exchange. Fig. 3l shows also the control equipment andauxiliary equipment including the l2-position rotary switch and itsassociated relays, and the inging interrupter.

Fig. 5 shows the code call apparatus including the lineswitches LSB andLSst associated with the code answering and code calling numbersrespectively and the code selector having wiper 507. This apparatus isaccessible to the connector shown in Fig. 3 through the banl: contactshown at the left of Fig. 5 and is operated in a mannerA to be explainedsubsequently. The lineswitches LS?) and LS are under the control et themaster switch shown in Fig. 2.

Mechanically, the master switch shown in Fig. 2 together with thelineswitohes LS1 and LS2 of the same drawing and the lineswitches LSSand LS1 of Fig. 5 are ot' the usual type, the plungers of thelineswitehes being preferably et theisel-re-storing type; that is, aplunger, when released, returns at once to the control ot the masterswitch rather than waiting for the master switch to return again to theposition from which the lineswitch was plunged.

The connector shown in Fig. 3 is mechanically of the well-known Verticaland rotary type having its bank contacts arranged in horizontal rows orlevels.

The apparatus having been described in general, a detailed descriptionof its operation will now be given; For this purpose it will be assumedthat the subscriber at substation A desires to converse with anotherlocal subscriber.

Local @all from substation A When the receiver is removed at substationA., line relay 203 of the lineswitch LS1 1 y nad energizes over the twoconductors of the calling line and the substation circuit in series andcloses a circuit through the pull-down winding of the lineswitch by wayot conductor 202, at the same time disconnecting the operating conductorfrom the succeeding lineswitches. The ground potential on conductor 202is obtained from the upper contacts of relays 307 and 304: of theconnector, Fig. 3, and through the high-resistance lower winding of thedelay-relay 201. As long as the high-resistance lower winding on thisrelay is unshunt-ed, the lineswit-ch is prevented from operating. Thedelay relay is slow to operate due to the high impedance oft its lowerwinding which prevents a quick building up of the current and due to theshortcircuited upper winding ot the relay, which winding is on thearmature end or tne relay and therefore prevents the magnet hun fromreaching the rmature quickly after it is built up. The delay relay isprovided primarily to take care of the situation which might arise incase a. lineswitch attempts to reoperate immediately after beingreleased, in which case it might plunge in on a t other than thatpreselected by the i switch if it were permitted tooperate before it hasrestored to the position of the master switch. TVhen relay 201 operatesit places the low-resistance upper winding in shunt of the lowerwinding, whereupon the pulldown winding 205 is magnetized sufficientlyto operate armatures 206 and 207, closin the connection through from thelineswitch to the trunl: comprising conductors 22-229 and disconnecting`line rela-y 203 and ground from the conductors or" the calling line.

Line relay 305 ot' the connector now operates over the calling linethrough conductors 226 and 229 oi the seized trunlr and conductors 219and 221 of the connector. Upon operating, line relay 305 closes acircuit for relay 306, whereupon the release relay 306 operates andcloses a ircuit for relay 307,

which relay, at its lower armature. places ground on the release trunkconducto thereby closing a holding circuit throu test wiper of themaster switch and over trunk conductor 227 and contacts of thelineswitch LS1 for the bridge-cutoff winding 204 of the lineswitch. Thiscir-cuit is established before the slow-acting` 203 has time to Jfallbaclr and it serves to maiutain the armatures 206 and 207 of thelineswitch operated.

As a further result of the operation of r lays 306 and 30'?` Fig. 3,thelswitch is pr pared for operation b3 Yf e lower armature of relay306, and ground is removed at the upper armature ot 307 from the delayrelay 201, which relay tails baclr in preparati n for the next callaFrom this it will be seen 4 that no further lineswitches can be operatedtime beino because ground potential is remove-d from the contact chainof the line relays.

The calling subscriber now hears the above-mentioned dial tone and dialstl e i rst digit inthe desired number, the digit 5, for example,whereupon line relay 305 reti-acts its armature ve times momentarily.Each time it does so, circuit is closed through the lower armature ofrelease relay 30G for vertical magnet 317, the circuit at the time ofits first closure including the lower associated' oli-normal spring, theupper spring 315, and the lower contacts of relay 303. By the operationof the vertical magnet, the wipers S22-325 are raised step by step untilthey stand opposite the ii'th level ot the baul; contacts. Relay 308 isvoperated in multiple with vertical magnet 317 upon. the first impulse ofcurrent, and, being slow acting,`it remains operated throughout thedigit, thereby inaintain'ng its own circuit and that of the verticalmagnet intact alter the oli-normal contacts have shifted, as they doupon the first vertical step. At the end of the verticalmovement, relay308 falls back and transfers the operating conductor from the verticalmagnet 31'? to the rotary magnet `When the next digit is dialled, thedigit 6 or example, line relay 305 is deenergized sinr timesmomentarily, transmitting an impulse to rotary magnet 319 each time itdeenergizes.

rlhese in pulses are transmitted through the lower armature of relay306, the two lower oit-normal contacts associated with ott-normalspring` 315, the lower armature, normal, ot relay 308, normally closedcontacts controlled by the lower armature of relay 310, and contacts ofrelay 312. Magnet 319 responds to these impulses and rotates the wipers322 325 step by step until they come into engagement with the sixth setof bank contacts (not shown) in the ifth level. Relay 311 is energizedin multiple with magnet 319 throughout the rotary movement and at itsinner upper armature it disconnects test wiper 323 from the test windingof switching relay 312 and connects it instead 'through interruptorcontacts 321 to the combined stepping' and busy relay 310, and at itslowerv armature it places a shunt around the associated contacts ofrelay 310 so as to prevent the interruption ot the rotary-magnetoperating circuit during the rotary movement in case relay 310 operatesduring such movement, due to a ground potential being engaged on a busytest contact by test wiper 323.

At the upper armature of relay 30'?, ground is placed on conductor 370.starting the ringinterrupter to operating as follows: `When theleft-hand winding of the operating magnet energizes through theassociated resistancery the reed is drawn to the lett,rwhereupon thediterential right-hand winding cnergizes in the opposite direction,causing the magnet to release the reed which swings to the right. rEheright-hand winding deenergizes and the reed is attractedagain. Theintern ittent current flow through the lower contacts of the reed, as itvibrates, passes through the primary winding of the associatedtransformer and induces the alternating ringing current in the secondarywinding.

Ground potential is extended from conductor 370 to the differential to erelay 363 through contacts of relay 312. Relay 368 buzzes at a ratherhigh rate and places a dial tone7 on conductor 221 through condenser335.

Ground potential is extended also to start relay 367 from conductor 370through the upper contacts of relay 311 and switch cam 355 inposition 1. The timing switch thereupon starts operating in a manner tobe later explained.

aZZefZ Zine busy energized over test wiper 323 by a ground' otentialwhen the wipers or" the connector come to rest on the bank contacts ofthe called line, and when relay 311`falls baci; the circuit ot rotarymagnet 319 and its own circuit is opened at the lower contacts oi therelay, thereby preventing further rotary movement of the connector inthe case of further opera-Y tion of the calling device at the callingsubstation. lt will be noted that relay 310 is now locked energized fromconductor 370 through its own inner upper armature, and the rotarymagnet interrupter contacts 321. It is tobe noted further that it isunnecessary to have the locking circuit of relay 310 controlled by relay311 to prevent relay 310 from locking up during the rotary movement, asis ordinarily done, because, in this case, the rotary magnet 319 opensthe circuit ot relay 310 on each step of the wipers. vWith lousy relay310 energized, a ground potential is extended 'from the groundedconductor 370 by way of the upper contacts of relays 311, 310 and 308 tothe junction of the winding of relay 368 and the associated resistance,by way of the upper contacts of interrupter relay 365. As a result,relay 363 is intermittently short circuited, as relay 365 pulls up andfalls back, causing it to give forth an intermittent buzzing soundinstead of a continuous buzzing sound heretofore given. Thisintermittent buzzing sound is recognized by the calling subscriber asthe busy signal. Upon hearing this signal, the calling subscriberreplaces his receiver, permitting relays 305, 306, 307, and 310 to tallback, and resulting in the release of the connector and of the callinglineswitch LS1. ln this case the master switch does not advance and inthe next call takes the same trunk.

alled Zine alle Assuming now that the desired line is idle when calledbusy relay 310 is not energized at the end of the rotary movement/andrelay 312 is operated instead, when relay 311 falls back and connectsthe upper winding oi'r' relay 312 to wiper 323. The circuit of relay 312eX- tends from the grounded conductor 370 by way. oit the contacts oi'relay 310 to the upper windingof relay 312, and thence by way ofcontacts or relays 311 and 312 to test wiper 323. The circuit iscomple-ted to battery through the cut-o winding of the calledline-switch, which winding is similar to the winding 204; of thelineswitch LS1. The energization of this winding results in theoperation orn the cutoil armature, corresponding to armature 206,clearing the called line of its attachments. Relay 312 operates overthis circuit and at its inner lower armature locks itselrl to conductor370, at the same time removing the operating potential from the tonerelay 368, whereupon the buzzing operation o1" relay 363 ceases and theapplication of the buzzing tone to the lower talking conductor no longertalles place. As a further result of its operation, relay 312disconnects the rotary magnet 319; at its inner upper armature itsdisconnects test wiper 323 from its own upper winding and connects itdirectly to ground so as to maintain the cut-off winding of the calledline switch operated; and at its upper and lower contacts it connects upthe wipers 322 and 325 to the ringing circuit. The lower wiper isconnected to the ringing lead 363, and the upper wiper is connected tothe upper winding of'ring-cut-oif relay 309. rlheV application ofringing current to the called line is accomplished in a way which willnow be explained.

Operation of timing switch It was mentioned hereinbefore that the timingapparatus, including the 12-position rotary switch, is started whenstart relay 367 operates from conductor 370 through contacts of relay311 and cam 355 when the switch is seized. `When it operates, relay 367locks itself to conductor 360 at its inner lower armature, and at itsupper armature it starts interrupter relays 366 and 365 operating.Relayl 366 closes a circuit for relay 365. R'elay 365 operates andshort-circuits relay 366, which relay then falls back, short-circuitingand open-circuiting relay 365. Relay 365 falls back and removes theshort circuit from around relay 366, allowing relay 366 to reoperate.This operation keeps up as long as relay 367 is operated. The operationis slowed down and is steadied by the copper collars on the armatureends ofthe cores of the relays, which are thereby rendered slow tooperate and slow to release.

Each time relay 365 operates it closes a circuit from the groundedconductor 360 for magnet 350. Each time magnet 350 falls i back, afterpulling up over this circuit, it advances the ratchet device one step,each step representing a separate one ot the twelve positions. Thepulses are delivered at a rate of about two per second.

The device is started when the connector is seized so that the connectormay be restored to common use at the end or about four and one-haltnseconds in case the second digit has not been dialled in the meantime.Such action results from the operation o ring-cut-otl relay 309 throughcam 354 in position 9 of the device and in a manner to be brought outhereinafter.

Now, when relay 311 responds to the second and last series of impulsesinthe number, during the rotary movement of connector and just prior tothe test which results in the finding of the line idle and the operationof relay 312 just described, it removes ground at its upper armaturefrom the interrupter start conductor 360, whereupon start relay 367falls back and closes a restoring` circuit for the timing switch byclosing a circuit for the stepping relay 364 through cam 352 (positions2 to 12) and the interruptor contacts 351 of magnet 350. Relay 364operates and closes at its lower armature a circuit Jfor magnet 350,whereupon this magnet operates and opens the circuit of the steppingrelay. The stepping relay falls back and permits the deenergization ofthe magnet, resulting in the advance of the timing switch one step. Whenthe magnet deenergiz'es the circuit of relay 364 is reestablished. Therelay and the magnet operate alternately in this manner until therestoring circuit is opened, when the switch passes beyond position 12and arrives in position 1. It will be noted that start relay 367 cannotreoperate t0 open the restoring circuit` until the switch arrivesinposition 1, owing to the fact that start relay 367, on falling back,opens its locking circuit. When start relay 367 reoperates, either rensponsive to the timing switch arriving` in its position 1 or to thefalling baclf: of relay 311 at the end of the second digit, whichevertakes place last, the interrupter relays 365 and 366 start driving thetiming magnet 350 again. Now, while-the timing switch is still inposition 1, ringing current from the secondary finding of the ringinginterrupter is placed on ringing lead 363, projecting ringing currentout over the calling line o-ver the lower contacts of relays 309 .and312, which ringing current returns by way of the upper line conductor,wiper 322, and the upper contactsA of relay 312 and 309 to battery byway of the upper winding of relay 309. r1`he slow-acting ring-cut-orelay 309 is not operated by this ringin@P current, as no flow of directcur- `ent takes place due to the inclusion of the usual condenser in theringing` circuit.

The ringing circuit is opened at cam 356 and lead 363 is groundeddirectly while the timing switch is in position 2, but in positions 3 to6 the ringing circuit is closed again and a further and longerapplication of ringing current takes place. The ringing current isapplied in this manner so that the particular telephone which is ringingmay be readily located when several telephones are mounted closetogether. The short preliminary ring calls attention to the call and thelong ring occurring shortly after enables the correct telephone to belocated.

A portion of the ringing current Hows back to the calling line throughthe small condenser 384, informing the calling subscriber of the ringingoperation.

The ring-cut-otl relay 309 may be operated over the called line in casethe called subscribed responds after 'the connection has been completedby the switching relay 312. W'hen operated in this way, relay 309operat-es through its upper winding over the called line and locksitself to conductor 370 at its inner lower armature. It relay 309 is notso operated, it is operatedk automatically by the timing device when itarrives in position 5. The circuit at this time is from ground by way ofthe'inner lower armature, operated, of relay 312, cam 353 off the timingdevice, conductor 359, and the lower winding of relays 309 to battery.Upon operating, relay 309 locks itself to conductor 370 at its innerlower armature; opens a point in the master-switch-st-art circuit at itsthird` armature from the bottom; disconnects the upperand lower wipersat its upper and lower armatures; thereby stopping the flow of currentto thecalled line; and at one of its lower armatures it places ground onconductor 224, thereby operating relay 304v to open a `further point inthe ground-supply connection to relay 201 (Fig. 2), and placing groundon thev pull-down wiper 324, closing a circuit through the bank contacton which wiper 324 is standing for the pull-down winding of the calledlineswitch, similar to wind- 205 of the lineswitch LS1. When thisoccurs, the lineswitch on the called line operates and connects thecalled line with the same trunk line with which the calling line isconnected, because the master switch is still standing in the sameposition. As soon as the lineswitch on the called line operates, itsupper winding is energized in parallel with winding 204 of thelineswitch LS1 from conductor 227 of the trunk, which winding serves tomaintain the lineswitch operated after the current flow through thepull-down winding has ceased. l

As a further result of the operation of relay 309, it closes at itsinner upper armature a. circuit from ground through the upper armatureof relay 306, through the upper armature of relay 301, the 30 and 00 camsprings,

and over vcut-E conductor 222 and the corresponding` wiper of the masterswitch for operating the cut-off and battery-feed relays 218 and 217ofthe trunk line over which the connection has been completed. Relay 218operates when this circuit is closed and locks itself at its inner'upper armature to the `grounded conductor 227, at the same time CIOopening its initial circuit; it disconnects conductor 226, 228, and 229of the trunk line from the corresponding conductors 219, 220, and221 ofthe connector at its upper and' at its two lower armatures; and atitsmiddle upper armature it extends the ground potential to the upperwinding of battery-feed relay 217. This relay is marginally adjusted anddoes not operate if the resistance 320 (Fig. 3) is included in itscircuit. Resistance 320 is, however, short-circuited at this time at theassociated contacts, with the result that relay 217 operates and locksitself to trunk conductors 226 and 229 at its upper and lower armatures,at the same time opening its initial circuit. Relay 217 now remainsenergized over the calling and called lines in multiple, supplyingtalking current to the transmitters through its windings. At its innerupper armature, relay 217 places a multiple ground connection on theholding conductor 227 so as to maintain both lineswitches operated and'so as to maintain a busy test potential on the corresponding contact inthe bank of the test wiper of the master switch.

The two subscribers may now converse with each other over theirrespective lines and through conductors 226 and 229 of the trunk line.

'onnectma release In the connector, line relay 305 falls back when thetrunk line is disconnected from the connector by relay 218, and relay306 falls back shortly thereafter, opening the circuit of relay 307,whereupon relay 307 falls back. The falling back of relay 306 removesground at its upper armature from cut-off conductor 222 and the fallingback of relay 307 removes ground at one point from release trunkconductor 223, leaving the lineswitches held up solely from the groundpotential supplied from the conductor 227 of the trunk at the innerupper armature of relay 217. At its upper armature, relay 307 preparesto replace ground on the pull-down conductor 202' 2), at the same timeremoving ground from the locking and start conductor 370, stopping` 'theoperation of the ringing interrupter and the relays associated with thetiming switch and resulting in the deenergization of relays 309 and 312.Start relay 367 of the timing switch now falls back and causes thisswitch to be restored to its normal position in the manner above pointedout.

With relays 307 and 309 deenergized, re-

lease trunk conductor 223 is connected through contacts of these relaysto the master switch start conductor 225, with the result that theground potential encountered by the test wiper lof the master switch,onthe test contact associated with conductor 227 of the trunk line,energizes the start relay of the master switch to cause the masterswitch to preselect another trunk line, as will be later explained.

Responsive to the deenergization of relay 306 of the connector,releasemagnet 318 operates through the associated oE-normal contacts 316and contacts of relay 305 and 306 and restores the connector to itsnormal position in the usual manner. The release magnet circuit isopened at off-normal contacts 316 when the normal position of the switchis attained.

Release of connection energize, whereupon the lineswitches restorel and,due to theirself-aligning plungers, come immediately to the control ofthe master switch opposite the instant preselected trunk. The connectionis now released and the apparatus is in readiness for use in completingsubsequent connections. j

Master switch operation The master switch is of the usual mechanicaldesign and advances to preselect trunksunder power supplied by theso-called U- spring shown just below the solenoid of the master switch.The master switch is shown in the position occupied just after thesolenoid has operated to align the plungers opposite the tenth trunkline, which is the trunk line shown in the drawings. Now, when the startrelay is operated through the test wiper and over conductors 223 and225, the groundcontrol conductor 224 is grounded at the upper armatureof the start relay so as to maintain the relay 304 of the connectoroperated during the masterswitch operation, and at the lower armatureofthe start relay a circuit is closed for the locking relay, whereuponthe locking relay operates and makes a further ground connection toconductor 224 and unlocks the associated segment, permitting theU-spring to advance the master switch to the next trunk line. If thenext trunk line is idle,A

the start relay falls back immediately, followed by the locking relay,stopping the master switch on the trunk. If, however, the trunk line isbusy instead of idle, the test wiper of the master switch encounters a.

ground potential on the test contact of the trunk line and the startrelay is maintained operated, and the advance of the master switchcontinues.

lVlien an idle trunk line is found, start and loclr relays fall bach,stopping the master switch on this trunk. `With the start and lockrelays both deenergized and with ringcut-off relay 309 of the connectordeenergized responsive to the preceding release of the connector, thecircuit of relay 30st is opened and this relay falls back, reconnectingground to the pull-down conductor 202 (lT ig. 2) through the delay relay201. The apparatus remains in this position until another call is made.

Assuming now that the master switch has advanced step by step until itis now standing on the first trunk line, and that a connection is set upinvolving this trunk line, the start relay operates in the heretoforedescribed manner upon the release of the connector after the connectionhas been set up. At this time, the trip relay energizes in multiple withthe locking relay through the associated linger-controlled contacts,held in engagement by the upper finger of the master switch. Uponenergizing, the trip relay loclrs the locking magnet to ground at itsright-hand contacts, and at its inner contacts it closes a circuit forthe solenoid of the inaster switch, causing the master switch to beoperated in a clockwise direction. The circuit of the trip relay isopened as soon as the master switch starts to move, but the springsremain mechanically loclred in their operated position by the lockingspring controlled by the lower finger of the master switch, which is nowout of engagement with such locking spring.v

When the master switch reaches the position shown in the drawings, thelower finger of the master switch unlocks the mechanically-lockedsprings of the trip relay, permitting them to open the locking relay andmaster switch operating circuit. lf this trunlr is idle at this time,the start relay is not operated and the locking magnet falls back.

Outgoing calls l one shown in the drawings and comprising conductors226*229, for example. TWhen this occurs the connector and other annav 1L .l ratus shown iii F ig. 3 respond as iiereinbefore described.

1When the calling subscriber dials the prey liminary digit 0, tenimpulses of currentare delivered to vertical magnet 317, whereupon thewipers 322-325 are raised step by step until they come to rest oppositethe tenth level of bank` contacts. lll/'hen the switch shaft carries thewipers up to the tenth level (the 0 level), the 0-level shaft springs313 are closed, ovrfierating` relay 303 from the grounded condenser 220by way ofcontacts of relays 303 and 301 and the 0level contacts 313.,Conductor 220k is grounded by way of conductor 228 and thecorresponding contacts of the lineswitch LS1. Relay 303 operates and atits middle upper armature removes the short circuit from around thewinding of relay 301 and extends the grounded conductor 220 by way ofthe eleventh-rotary-step spring 314 and its right-hand contact,innerupper armature, operated, of the relay 303,

and the interruptor contacts 321 to steping relay 310. This circuit iscompleted )ust at the end of the last vertical step and while theslow-acting relay 308 is still energized in multiple with verticalmagnet 317. Stepping relay 310 operates over this circuit and locksitself to conductor 370 at its inner -i upper armature, at the same timepreparing a circuit for rotary magnet 319 at its lower armature. Relay301 energizes in series with relay 303 responsive to the removal of theshort circuit from around relay 301 by relay 303, and removes the shuntfrom around resistance 320 in the cut-olf lead. lncidentally, relay 301locls itself at its inner upper armature to battery through the innerupper contacts of relay 306 and the associated resistance, therebyshunting this resistance around relay- 303, but this operation has noparticular effect at this time.

Villien the slow-acting relay 3,08 falls back, it opens the initialcircuit of relay 310 at its inner upper armature .and completes the cir-.cuit of the rotary magnet through the lower armatures of relays 3i0 and312. Relay 310 remainsloclred up at its inner upper armature toconductor 37 0 so as to maintain the rotary magnet circuit closed.Responsive to the energization of the rotary magnet 319, the wipers322-325 are rotated into .engagement with the first set of bank contactsin the tenth level. Relay 311 is energized in parallel with the rotarymagnet and transfers test wiper 323 to the 'circuit of steppingy relay310 at its inner upper armature. lNear the end of its stroke, rotarylmagnet 319, at contacts 321, opens the circuit of relay 310, whereuponrelay 310 falls baclr and opens the rotary magnet-circuit, causing therotary magnet to fall back and close contacts 321 again.

lf the trunk line terminating in the first set of contacts in thetenth'level is busy, ground potential is encountered on the tenthcontact of said trunk line by wiper 323, operating the stepping relay310 again. Relay 310 again operates magnet 319, causing the wipers totake another step. rllhis alternate operation is repeated as long as thewiper 323 engages busy contacts, and if all the trunk lines are busy theoperation continues until the wipers have been advanced to theeleventh-rotary-step position, operating spring 314, which opens a pointin the rotary magnet circuit and connects the grounded spring to thecircuit of relay 310 through contacts 321, maintaining Arelay 310operated so as to send back the interrupted busysignal from the tonerelay 368 after relay 311 falls back, as Y hereinbefore described. Theeleventh-rotary-step contacts above and slightly to the left of relay301 operate to shunt resistance 320 so that the battery-feed relay ofthe trunk line may operate over conductor 222 in case the callingsubscriber does not hang up, but waits until after the switchthroughoperation occurs responsive to the .above-described operation ofring-cut-off relay 309 in position 5 of the timing switch.

Assuming now that the trunk line extending from the 0-level bankcontacts shown in the drawings through terminals 256-257 to thelineswitch LS2 is found to be idle, wiper 323 does not encounter` groundpotential on the corresponding contact thereof and relay 310does notenergize again after the wipers have come to rest on the contact set.

ln this case, the deenergization of the slow-A acting multiply relay 311is followed by the cnergization of relay 312 through its upper winding,over the conductor extending through terminal 256 and thecorrespondingly numbered terminal of Fig. 2, conductor 127, and the busylamp shown in Fig. 1 t0 batt-ery. The busy lamp becomes lighted andrelay 312 operates, performing` the functions described hereinbefore.With relay 303 operated, the closing of the locking circuit for thelower winding of relay 312 closes a multiple circuit for the lowerwinding of relay 309 through the upper contacts of relay 303. Belay 309thereupon operates and performs the functions hereinbefore describedincluding the grounding of the pull-down wiper 324 to cause thelineswitch on the called trunk to operate and grounding the cut-offlead222'at its inner upper armature.

l/Vhen wiper 324 is grounded, a circuit is closed-through terminal 257for the pulldown winding 211 of the lineswitch LS2, operr-ting thelineswitch to disconnect the line relay 209 and to make connection withthe trunk line comprising conductors 22S- 229. rlhe springs of theplunger arms 212 connect up the grounded B. C. O.` (bridge-cutoff)conductor 126 to the B. C. O. winding 210 so as to hold the lineswitchoperated. Vhen switch LS1 operated.

ground is placed on conductor 222, it is obtained through the resistance320 on account of the fact that relay 301 is now energized, and,although relay 218 of the trunk is able to energize and lock Iitselftoconductor 227, the marginally adjusted line relay 217 does notenergize when the operating conductor is eX- tended to it because of thepresence of the resistance 320 in series with the conductor.Consequently, the battery feed is no-t connected up locally and thecalling subscriber is thereby enabled to operate the switches in themain exchange directly by his calling device, as will be subsequentlypointed out.

lNith the lineswitches LS1 and LS2 both operated, the bridge ofsubstation A across` the line thereof is effective in producing acurrent flow over conductors 125 and 129 (associated with the lineswitchLS2) and through the local trunk line conductors 226 and 229. Conductor129 is connected to ground in the trunk circuit TC through contacts ofrelays 116 and 117, and conductor 125 is connected to battery in themain exchange through contacts of relay 117 in the trunk circuit TG,relay 114 of the trunk circuit TC, contacts of switching relay 102 ofthe lineswitch LS at the main exchange, and line relay 101. Series relay114 operates in this conection in series with line relay 101 and closesa circuit for release relay 115, whereupon relay 115 places a groundpotential on release trunk conductor 127 so as to maintain theinter-exchange trunk line busy to the connector. Abranch connectionexists through the upper contacts of relays 119 and 120 to the B. C. O.conductor 126, holding ground being thereby extended through contacts ofthe lineswitch LS2 to the release conductor 227 of the local trunks,maintaining relay 218l of the trunk and the winding 204 of the line-This operation ofrelay 115 occurs, of course, before the release of theconnector, initiated by the action of relay 218 in disconnecting thetalking conductors of the trunk line from conductors 219 and 221, takesplace.

Relay 116 operates over the lower talking conductor and through its owncontacts and those of relay 115, and locks itself to ground locally, atthe same time switching the lower ktalking conductor through andremoving ground from the right-hand section thereof. In the mainexchange, the operation' of line relay 101 results in an idle trunkbeing selected in the usual manner by the lineswitch LS, this lineswitchbeing operated by the selfinterrupting magnet 103 under the control oftest wiper 105. When an idle trunk line is reached, relay 102, which isshort-circuited by the `round potential encountered by wiper 105 duringthe operation of the lineswitch, is no longer short-circuited andenergizes in series with the relatively low resistance magnet andswitches the connection through to the wipers -1-106. Line relay 101 isdisconnected, and the connection is extended through the line relay ofthe associated selec? for relav 102 before the slow-acting relay 101 hashaddtiine to fall back.

In the branch exchange, the master switch is to advance in thehereinbei-ore-described manner when relays and 309 have both fallenback, and another idle trunk line is preselected, leaving the connectionestablished rom the line of substation A to the main exchange throughthe lineswitches LS1 and LS2 and the trunk line TL.

The subscriber at substation A now dials the various 1listed Vdigits inthe number of the desired subscriber, whereupon the main eX- k changeswitching mechanism operates to complete the connection in the usualmanner.

When the subscriber` at subst-ation A replaces his receiver afterconversation, the

main exchange connection is released in the f; usual manner and theseries line relay 114 in the trunk circuit TC falls back and opens thecircuit of release relay 115. Release relay 115 falls back after asliO-ht interval and removes ground from conductor 127, whereupontheline switches LS1 and LS2 release and cut-off relay 218 falls back.

Attempted 'main exchange caZZ from restricted f il restricted to therestricted class by removing the'jumper associated with the liiieswitchspring which contactsY with the bankl contact connected withdiscriminating conductor 22S. In this case conductor 228 is not groundedwhen the lineswitch LS1 is operated upon the removal of the receiver andconductor 220 of the connector is therefore not grounded. Now when thedigit 0 is .dialledy relays 301 and 303 operate in series throughcontacts 313, and relay 303 extends conductor 220 through contacts ofthestilloperated slow-acting relay S and interrupter contacts 321 tostepping relay 810. Relay 303 places a ground potential on conductor 220from the grounded conductor 223 through resistance 302 so as to operaterelay 310. Relay 310 operates throughresistance 302 and locks itself toconductor 370. Then, when relay 308 falls back to start the rotary`inoif'ement, it transfers conductor 220, at its upper armature, to therotary magnet 319 through contacts ot' relays 310 and 812. Rotary magnet319, however, will not operate through resistance 302, andV relay 310remains "ie of substation A is changed 'from the un-v operated, givingthe calling subscriber a busy signal in the hereinbefore describedmanner.4 The connector is released by the calling subL scriber or by thetiming device in casethe calling subscriber does not hang up.`

s Incomz'fngfcall from main circ/imagel Assume that the trunk line TL isseized'in by a connector switch of the usualtype.

Vfhen this is done, the connector places' ground on private-normalconductor 108', op-

erating relay 102 su'tlticiently to cause its up? per armature springsto move out of engagement with their resting contacts, but therelay dcesnot operate suiiiciently to cause the wipers to be connected up owing tothe usual mechanical interlocking arrangement (not shown) between thearmature ot relay 101 and the armature of relay 102.

Make-busy relay 111, which isV bridged across the trunk-line conductorsthrough contacts of relay 115 and in series with the high resistance110, energizes from the battery potential superimposed on the ringingcircuit (not shown) so as to make the trunk line busy in the branchexchange by grounding conductor 127, no matter whether the connection ismade to the trunk line during the ringing period or during the silentperiod. The

high resistance 110 limits the current How to such a value that thering-cut-OE relay (not shown) will not operate. Y'

VVhenringing current is sent over the talking conductors of the trunkline TL by' the connector, it operates the ring-up relay 112 of trunkcircuit TC, whose lower winding -is bridged across these conductorsthrough the associated condenser, lower contacts of-relay 112, and thelower contacts oitl release relay' 115. Upon operating, relay 112, atits upper armature, closes a locking circuit for'itself' throughcontacts of relay 118. At its lower armature, it removes 'its lowerwinding from in bridge of the talking conductors, and, at its innerlower armature, it operates relay 113, which makes a second groundconnection to conductor 127. Thel second connecl' tion to conductor 127at the upper contacts of rela-y 113, is of utility during the ringingperiod,'as it maintains conductor 127 grounded uninterruptedly, eventhough relay 111 lutters responsive to the ringingcurrent.

113 closes a circuit for the call'lamp at the att-endants switchboard atits inner upper armature through contacts of relay 118,*and` at itslower armature it makes certain circuit changes so that the ring-cut-oftoperation 'to be later performed in the calling connector willbecontrolled over a loop circuit without any local groundedconnectionsto the talking conductors. I

1V hen the attendant notes the lighted con- As a further result of itsoperation, relayyro ' as TC, thereby supplying a ground potentialthrough relay 401 to conductor 137 and through contacts of the relay topick up conductor 136. The vtalking circuit of the telephone isbridgedacross the associated talk-` ing conductors. The operator now throwsthez combined release and connect key, individual to the trunk circuitTC into connect position, thereby extending ground from pick-.upconductor 136 to the lower winding of connecting relay 117. Relay 117operates and locks itseli: through its upper winding and through theinner. upper contacts of re.- lay 120 to the common holding conductor137. Guard relay 401, Fig. 4, new operates in series with theV upperwinding of relay 117, Eig, 1, and disconnects ground4 from piel'- upconductor 136, thereby preventing the operator from operatinganotherconnecting relay such as 117 until such time the op.- eratorVdisconnects by hanging up her receiver or releases the connection bythrowing the combined-release and connect key into release position. g

The eperator restores the key after she has yoperated it momentarily,leaving relay 1.17 locked up as above mentioned. 1.Vith relay 117operated, it will be noted that the talking circuit is split and thatconductors 125l and 129 extending to the `lineswitch LS1 are connectedto common conductors 133 and 134, and that the main-exchange talkingconductors are connected at the upper and lower armatures of the relayto commonconductors 130 Vand 131. this time, ccnductor131 is joined tothe lower main-exchange talking conductor throughv the lower armature ofrelay 117 and the v lower armature, operated, of relay 113.

Upon reference to Fig;y 4, it` will be noted that the commen talkingconductors 130 and 131` are joined through contacts of the dial key to,`conductors133 and 134 and that the j cined talking conductors varebridged by the impedance 402 and bythe talking bridge ofl the attendantstelephone. The usual ring-v cu-tfoii operation is now performed in thecalling connector responsive to current over the upper talking conductorthrough rela1 114, through impedance 402 and the'attencints telephone inparallel., and back over the lowertalking ccnductor. At the same time,thel usual ring-cut-o relay oi. the seizing connector responds so as todisconnect. The Vusual talking-currentsupply connections are substitutedfor the ringing connections.

Relays 1714, 115, and 1,16, pull up one after the other (as in thehereinbefore-described outgoing call) as relay 114 receives current inseries. with the lett-hand section ot the upper talking conductor.

Relay 113 being operated 118 at its inner ylower armature, whereuponrelay 1,18 operates and locks itself at its inner lower armature throughthe lower contacts of release relay 120. At 'armature 141, relay 118prepares'a 1circuit for line relay 209 of the lineswitch LS2; itprepa-res a circuit or the supervisory lamp of the trunk circuit at itsupper armature; and it extinguishes the call lampl at its inner upperarmature by removing the shunt from around the resistance associatedwith armature 122 of the operated connect relay 117.

Having caused her position equipment to be connected with the trunkcircuit TC in the above manner, the operator learns the desirednumber-'from the calling subscriber and then throws her dialfin key,shown in Fig, 4, thereby disconnectingjthe impedance 402 and theextendedV main exchange talking conductors 130and 131`fron1 the'extendedbranch @Xchange talking conductors 133 @c1134. leaving her telephonebridgd across conductors 133 and 134. At the upper contacts of thekey,ground is placed on Vconductor 132, closing a.V circuit through armature141 of relay 118, lower contacts of relay 119, conductor 128, andthelineswitch cut-olcontacts for line relay 209. Relay 209 pulls up andoperates the lineswitch to seize a trunk line, the trunk line comprisingconductors 226.-. 229 for example. Responsive to the operation of thelineswitch, the B. C. O, `winding 210 is energized as a holding windingthrough the associated contacts of the lineswitch from the groundpotential placed'on conductor 126 in the trunk circuit TC through theupper contacts of relays 119 and 1 20 from the grounded conductor 127.vAs a further result of the operation of the lineswitch, the groundedconductor 126- is extended through the bank of theV lineswitch tcrelease trunk conductor227, thereby making the trunk busy in the masterswitch'hank and closing a circuit over conductor 223 and contacts ofrelays 307 and 309 of Ythecennector for the start relay of the masterswitch over` conductor 225. The start relay, being stiiljly adjusted-Yenergizing' over conductors 219 and 221 through the attendants telephonewhich is now connectedto the incoming talking conductors 125 and 129` asabove pointed out@ 1n case diiiiculty is experienced in preventing thestart relay fromenergizing, its .Circuit may be altered to include an.added'pair of normally closed contacts on delay relay 201.

The operator now dialsthedigits in the desired number, whereupon theconductor is set on the line of the called subscriber, the

line of substation A for example, in which case the substation A issignalled by ringing current, after which the lineswitch LS1 is operatedthrough wiper 324 of the connector and through terminal 253 when theringcut-oif relay 309 operates. Ground is placed on cut-ofil conductor222 at the inner upper contacts of ring-cubed relay 309 to operate relay218, Fig. 2, through the cut-off wiper of the master switch, butbattery-feed relay 217 is not operated at this time owing to the factthat the resistance 320 is inserted into the circuit owing to theprevious operation of relay 301 ovei conductor 220 from the batl teryconnection supplied at the contacts of the lineswitch LS2 for thatpurpose. Relay 301 is locked at this time through its own contact andthe inner upper contacts or relay 306 to the associated resistance, andits initial circuit is opened. The result of this is that the batterysupply for talking purposes comes to the called substation A from themain exchange rather than from the branch exchange, this being inaccordance with well- '1 established practice.

In case the operator, during the setting up of a local connection,discovers that she has made a mistake in dialling, or, for any otherreason, wishes to release the connector and start over again, shepresses the releasein key, Fig. 4, opening the line circuit at the lowercontacts of the key and grounding coir i ductor 135 at the uppercontacts of the key so as to operate the release-in relay 119, Fig. l,through armature 12.3 of relay117. Relay 119 disconnects ground from thelineswitch private normal conductor 126 at itsvvupper armature and opensa point in the line relay circuit at its lower armature. YVhen the keyis released, the restored lineswitch ree-peintes and the connector isprepared for operation as hereinbefore explained.

Having dialled the local number, the oper` Aator restores the dial-inkey, reconnecting the two sections of the talking circuit together sothat the subscribers may converse.

After listening in, either before or after restoring the dial-in key, tomake sure thatthe desired subscriber has responded, the operatorreplaces the receiver on her telephone,

opening the locking circuit of the upper winding of connecting relay 117of the trunk circuit TC. Relay 117 falls back and connects the twotalking sections together and er hangs up. This bridge is effective, incase the operator hangs up right after dialling, to hold the connectorinthe branch exchange operated until it is released responsive to theoperation of the timing device or to the response ofthe calledsubscriber. Relay 118 remains locked up through its own inner lowercontacts and the lower contacts of relay 120. f When the calledsubscriber replaces his receiver at the end of the conversation, linerelay 114 falls back and opens the cir-cuit of release relay 115, whichrelay falls back and lights the supervisory lamp through contacts ofrelay 118. When the calling subscriber hangs up, the connector in usereleases (unless it is of the release-by-lastpa'rty type),

permitting relay 102 to restore and connect up line relay 101 of thelineswitch. Line relay 101 does not operate at this time, even thoughrelay 111 is bridged across the talking conductor of the trunk lineowing to the fact that there is no operating ground potential connectedto the lower trunk line conductor.

When the operator n otes the lighted conrelease-connect key in releaseposition, operating relay7 120, bringing about the release of relay 118.rlhe lineswitches LS2 and LS1 rei lease and relay 218 falls backresponsive to the removal of ground potential from the conductor 126 atthe upper contact of relay 120. The entire connection is now releasedand the apparatus involved therein is in-readin'ess to be used insetting up further connections.

Setting up a tail-todae? connect-0n with such trunk is caused to operateto connect such trunk with the calling line. Assum` ing that the numberof information trunk #1 is dialled, and that this trunk isidle at thetime and is accordingly seized, the call lamp associated therewith isoperated over the priV4 vate normal conductor in parallel with thebridge-cut-oft' winding of the lineswitch, corresponding to winding 204ofthe lineswitch LS1. 1 Upon` noting the lighted condition 'of -the calllamp, the operator respondsby momentarily operating the answering keyassociated with relay 403, whereupon relay 403 operates throughtheswitchhook contacts' ofthe attendant telephone and through contacts ofrelay 401 and locks itself in series with the said relay. Relay 403disconnects the private normal conductor from' the call lamp andconnects it to ground instead, although theY latter is not essential asthe connection is being held up by the battery-feed relay of the trunkinuse, corresponding to battery-feed relay 217, Fig. 2. At its upper andlower contacts, relay 403 connects the conductors of the informationtrunk to the operators talking circuit, enabling the attendant toconverse with the calling subscriber. Upon being informed as to thecalling s'ubscribers desires, the operator replaces the receiver on theassociated telephone, whereupon relay 403 falls back. The connection setup from the line of substation A is released when the calling subscriberhangs'up.

In order to complete the connection .to the desired main-exchangesubscriber, the operator removes the receiver from her telephone andobserves the busy lamps associated with the various trunk circuits suchas the trunk circuit TC', and throws the connect key of an idle one, theone of trunk circuit TC for es ample, whereupon relays 117 and 118operate as before described, and relay 117 connects the two sections,respectively, of the trunk to the operatorsset over conductors 130 and131, and'conductors 133 and 134. When the bridge across conductors 130and 131 is placedacross the trunk conductors extending to themainexch'ange, there is a ground potential encountered by conductor 131`through contacts of the operated relay 117, and contacts of theunoperated relays 113 and 116. This ground potential is transmitted overconductor 131 and through imi pedance 402, Fig. 4, to the upper trunkconductor'over conductor 130, to operate the line relay 101 of thelineswitoh LS in the main exchange. Relays 114 and 115 are operated, asbefore.

through the lower winding of the line relay of the selector is placed onthe lower talking conductor of the trunk line TL operating relay116through its own inner lower contacts, contacts of relay 113,and-armature 142 o of relay 11S. Upon operating, relay 116 locks itselfenergized independent of the lower talking conductor and joinsthe lowertalking'conduct-or of the trunk line TL to the `lower left-hand talkingconductor 129, at the Sametime removing the local ground connectionfromv the lower talking conductor.

In order to be able to operate the mainexehange switches to set up theconnection to .the called line, the operator throws her dialscriberresponds to the call,'the attendant in- When an adle selector is seizedby the lineswitch LS, ground potential forms him that the subscriber atsubstation A desired to converse with him and requests him to waitamoment while she completes the connection.

The operator thereupon releases her dialout key, throws her dial-in key,causing the lineswitch LS2 to operate in the manner describedheretofore, and dia-ls the number of the subscriber at substation A,whereupon the connection is extended to his line in the mannerhereinbefore described. It will be noted that the impedance winding 402associated with the dial key, Fig. 4, is placed across conductors 130and 131 so as to hold the mainexchange connection while the operator isdialling the local number of the subscriber at substation A.

From this point on, the connection is handled in the manner describedvhereinbefore in connection with the description of the handling of anincoming call.

The 00de @all equipment In explanation of the code call equipment shownin Fig. 5, it may be pointed out that in a private establishment itoften happens that there are a number of employees who are called quitefrequently and whose work f scriber removes his receiver and dia-ls thecode-call number 30, followed by the particular code digit assigned tothe person in question. Assuming thatthe calling subscriber is the oneat substation A, Fig. 2, the removal of the receiver results in theoperation of lineswitch LS1 to seize a trunk line, the one shown in thedrawing for example. The common connector shown in Fig. 3 is prepared ifor operation in the usual manner; is raised up with the third level ofbank contacts when the first digit 3 is dialled; and is rotated intoengagement with the tenth set of bank contacts in the third level, Fig.5, when the second digit 0 is dialled. The contacts associated withresistance 320 and labelledv 30 and 00 are separated at this time by theusual cam arrangement on the shaft ofthe switch, thereby inserting' theassociated resistance 320 into circuit with the switching conductor 222so as to prevent the subsequent operation of the battery feed relay 217.Assuming that the code call number is idle at this time, switching relay312 of the co1mecl tor pulls' up in the usual manner over test wiper 323through the bridge-cut-off windingV In order to transmit the calls topulling up of relay 312 the usual locking circuit is closed for thelower windingthereof from conductor 370 and a parallel circuit is nowclosed for the lower winding of ringcut-oii relay 309 through theassociated cam springs labelled 30 and 00. Relay 309 operates and placesa ground potential on wiper 324 thereby closing a circuit through thesaid wiper and the banlrcontacts on which it is standing for thepull-down winding of the lineswitch LS'c, operating the lineswitch LS4:to extend a connection to the same trunk line with which the lineswitchLS1 is connected. Cut-ofi" relay 218, Fig. 2, is operated in the usualmanner, but the marginal relay 217 is not operated owing to the factthat resistance 320 is inserted in circuit at this time by theassociated cam springs as above pointed out.

Line relay 501 of the code selector now operates over the associatedtalking conductors and the corresponding conductors of the trunk line inuse by the lineswitches LSA and LS1 and over the line of substation Aand closes a circuit for the associated release relay 502 which operatesand places ground on the associated release trunk and private normalconductor so as to hold up the two lineswitches and cut-off relay 218.This ground potential is placed on this conductor prior to the removalof ground potential therefrom through wiper 323 of the connector. Relay502 also prepares the code selector for operation at its lower armature.

Then the calling subscriber dials the code digit assigned to theparticular desired person, line relay 501 falls back a correspondingnumber of times and operates the rotary magnet of the code selector eachtime it falls back. Relay 503 operatesin parallel with the rotary magnetwhen the first impulse is received, and, being slow-acting, remainsoperated through the series of impulses. lVhen relay 503 falls back atthe end of the digit it closes a circuit through contacts of relay 504and through off-normal contacts O. N. for starting the motor of the codegenerator and for supplying a ground potential through the cam contactsof the generator to the various bank contacts. The motor now operatesthe cam contacts to generate their respective codes in the usual mannerand the selected code is supplied through wiper 507 to the code bellsthrough the contacts on which wiper 507 is standing.

Assuming that the person called fails to respond, the calling subscriberreplaces his receiver whereupon line relay 501 falls back followedshortly by the deenergization of relay 502 to permit the release of theconnection when it removes ground from the associated release-trunkconductor.

lVhen thed-esired person hears his code being broadcast throughout theplant, he

proceeds te the nearest telephone,

removing the receiver and obtaining control of the connector in theusual manner through the operation of the lineswitch on the telephone inuse, dials the code-answering number 39, whereupon the connectorconnects with the line-switch LS3. The switching relay 312 of the.Lconnector is operated at this time in series with the B. C. O. windingof vLS3, and connects up Wipers 322-a'nd 325,

ing ground from the start conductor of the code generator as well asoperating the release magnet to restore the wiper 507 to normal. Thecircuit of the release magnet is opened at the off-normal contacts ofthe switch when the wiper 507 reaches its normal position.

In the connector, ring-cut-o relay 309 energizes at thersame time thatrelay 504, Fig. 5, energizes and it locks itself at its inner lowerarmature and performs the functions hereinbefore described, includingthe grounding of the cut-off conductor 222 to 'cause the cut-olf andbattery-feed relays of the trunk in use, corresponding to relays 218 and217, Fig. 2, to operate to isolate the trunk and to connect up a sourceof transmitter-supply current.

The conversation now takes place between the-line of substation A andthe line used by the called subscriber in answering the code call, theswitching apparatus included in the connection being the lineswitch LS1which is plunged in on the trunk comprising conductors 226-229, thelineswitch LS4 which is plunged on the same trunk, the lineswitch LS3,and the line'switch of the answering line, which is plunged in on thesame trunk as the lineswitch LS3.

After the conversation is over, the lineswitch LS3 and the lineswitch ofthe answering line are both released when the an- EL uc to its normalposition. Relay 502 also un- .gronnds the associated release trunkconductor, permitting the lineswitches LS4 andv LS1 to restore, andpermitting the cut-ofi' relay 218, Fig. 2, to fall back.

The branch exchange has been described Vhereinbefore as of one V10G-linecapacity. The circuits of the connector shown 1n Fig. 3,

however, have been arranged so that they will function in connectionwith a modified bank arrangement when a private automatic exchange ofthis character is arranged for a capacity not to exceed fifty lines.

vVhe'n the exchange is arranged to have an `ultimate capacity of onehundred lines the section may be installed, in which case the twol wipersetsare adjustedcloser together, so that when `the bottom set isVopposite the first bank level the top set is opposite the sixth level.The bottom'lwiper set uses the lower half of the bank while the upperwiper setl uses the upper half of the bank. n

In this case only live lirstfdigits are required and it is thereforeconvenient to assign the digits 2 to 6 rather than the digits 1 to 5, onaccount of the fact that the digit 1 is often undesirable owing to thedanger of preliminary impulses and faulty line conditions giving the4effect lof the dialling of the digit 1 before the dialling operationstarts, this condition being well known and generally understood. Thewiper sets are therefore adjusted so that they will come Ophosite thelevels 1 and 6 of the bank when the digit 2 is dialled and will notextend a connection to the talking conductors of any called line ifraised only one step. The reason is that the wipers 322 and 325 of theconnector are the wipers of the lower set and do not engage with anybankcontacts, while the wipers 323 andl 32d ofthe upper setfengage withbank contacts in the fifth level, whichV is the upper levely of the linecontactsand are therefore not -connected up, being left dead, as are theO-level contacts of wipers 322 and 325 in Fig. 3. Y In casegthearrangement were usedin connection .withoutgoing trunk lines thatrequired the line contacts of the bank to be connected up, the wipers322, and 325 would then be placed in the upper set and wipers 323 and324 would form the lower set. In

this case, wiper 323 would not engage a bank contact `*when the lirstdigit is 17 and switching relay 312 would not operate to connect upwipers 322 and 325.

For many years, it has been standard practice to assign .the digit totrunk lines outgoing from a private` automatic exchange, for whichreason it is desirable to assign the digit 0 even in the modified50-line private automatic exchange above described, even though thedialling of the digit 6 is suliicient to cause the seizure of onev ofthese trunk lines. In Fig. 3, it will be `noted that the circuit ofvertical magnet 317 includes con-k .tacts of relay 303 which is operatedthrough thel associated 0 level shaft springs 313. When the 10U-linevprivate automatic exchange is used, the lower contacts of relay 303perform no useful function, but, when the private automatic exchange,modified as above outlined, is used, the springs 313 are jarranged tooperate when the shaft is raised six steps, whereupon relay 303 operatesand opens the circuit of the vertical magnet thereby preventingv the-wipers from advancing above the outgoing trunk level.

Yvlhat is claimed is:

1. In a telephone system wherein each of a plurality of lines isprovided with a single individual' line switch, trunk lines accessibleto such line switches, means controlled over a calling line for causingthe line switch individual to such calling line to seize an idle one,ofvsaid tru-nk lines, a-nd means including directive switchingmechanism normally connected ,multiple to each of saidr trunk linescontrolled over the cal-ling line for causing the line switch individualto a desired'called line to complete a talking connection between thecalling and the called lines by seizing the same trunk line previouslyseized by the line switch individual to the calling line. l

2.*In a telephone "system wherein the line switches individual,respectively, to subscribers lines are presided over by a single masterswitch and have access i-n common to a group of trunk lines, meanscontrol-led over any trunk line after such trunk line has been Seizedlby a line switch Aof a calling line to complete -a'` talking connectionbetween such calling linel and a desired called one of said lines., bycausing the line switch: individual tgosaidcalled line-to seize-the sametrunk` line previously seized by the line switch of the calling liner.v

3. Ingfa: telephone 'system wherein the line switchesindividual,respectively, to the lines entering the exchange are presided over by acommon master switch which causes them all to normally prcselectsingleidle one of a plurality of trunk-lines accessible thereto incommon, means for maintaining the master switch and the idle lineswitches at rest vwhen a line switch is `operated over a calling line toseize the preselected trunk, and means conlll() trolled over the callingline and the seized trunl line for completing a talking connectionbetween the calling line anl a. desired called one of said lines byoperating the switch ot the called line to seize the s` trunk line.

4. In a telephone system wherein the line switches individual,respectively, to the lines entering the exchange are presided over by acommon master switch which causes them all to normally preselect asingle ille one ot' a plurality of trunk lines accessible thereto incommon, means for maintaining the master switch and the idle l' ieswitches at rest when a line switch is Voperated over a calling line toseize the preselected trunk, means controlled Aover the calling line andthe seized trunk line tor completing a talking connection between thecalling line and a desired called one of said lines by operating theline switch ot the cal ed line to seize the same trunk line, and meinsfor thereupon operating the master switch to cause the remaining idleline switches to preselect anotner idle trunl line.

5. In a telephone system, a line having a line switch individualthereto, a 'plurality ot trunk lines'accessible to said line switch, andmeans for operating said line switch to seize a preselected idle one ofsaid trunk lines to initiate a call outgoing trom'said line and foroperating said line switch to seize particular one of said trunk linesto complete a'call incoming to said line.l

6. In a telephone system wherein each line entering a central exchangeis provided with a line switch individual thereto, a plurality of trunksaccessible to said line switches in common, switching mechanism in thee5;- change, means for operating any line switch either yer the line towhich it is indi f'idual or through the said switching mechanism in theexchange to seize one et said trunk lines, and a master switch common toall aid line sv tches for predetermining the trunlclines with which theline switches connect so that the lines of operated'line switches aretelephonically connected together in pairs.

In a telephone system wherein switching mechanism is provided torconnecting any one of a number of subscribers lines to any one of aplurality of trunk lines, an automaticV connector switch having accessto all said lines and normally in association with said trunk lines incommon, means foroperating said connector switch over a calling lineand-over one ot said trunk lines to effect a connection between thecallingline and another line through said trunk line and independent ofthe connector switch, and Vmeans for thereupon isolating said trunk linefrom said connector switch while leaving the other trunk lines inassociation therewith.

8. In a telephone systeinwherein acht rality et trunk linesniay be byswitching mechanism to any one cfa plurality of subscribers lines, asingle automatic connector switch normally connected to each of saidtrunk lines, means tor operating said connector switch overacalling lineand over one ot saidtrunh lines to complete a connection, and means forthereupon disconnecting trunk line from the connector switch, leavingthe remaining trunk lines connected thereto.

, 9. In combination, a plurality of telephone lines, an automaticconnector switch'having access thereto, a plurality of trunk lines eachnormally connected to sad connector switch, and non-numerical switchingmeans for connecting any calling one ot the first-mentioned lines to anyone of said trunk lines.

l0. In combination, a plurality of telephone lines, an automaticconnector switch having access thereto, a plurality ottrunlr lines eachnormally connected to .said connector switch, and non-numericalswitching means operative to connect any calling or any called one ofsaid lines to any one of said trunk lines. l

l1. In a telephone system, an automatic connector switch, a trunk' linenormally connected thereto, means jor extending a calling line to saidtrunkY line', means controlled'rover the calling line tor-,operatingsaid connector switch into association with a called line, ns forcompleting a connection between the calling and called lines over acircuit path independent of the connector, a cut-od relay individual tosaid trunk line, and means effective upon the sa-idcompletion of theconnection for operating said cut-oli" relay to isolate `vsaid 'trunkline from said connector switch. Y Y' f 12.111 a telephone system, anautomatic connector switch, a trunk line normally connected thereto,means for extending a calling line to said trunk line, current-supplycon nections in said connector switch for supplying transmitter currentYto theV calling line, means cont-rolled over the calling line foroperating said connector switch into association with a called line,means for completing a connection between the calling and called linesover a circuit path independent of the connector, a cut-ott' relayindividual to said trunl'line, means effective upon the said completionof the connection for operating said cut off relay to isolate said trunkline from said connector switch, a current supply relay in said trunkline, and means for connecting such relay to the trunk line to supplytransmitter current atter the trunk line has been disconnected from theconnector.

13. In a telephone system, an automatic connector switch, a trunk linenormally connected thereto, inea-ns for extending a calling line to saidtrunlz line, means controlled over the calling line for operating saidcon-

